5 Answers

Probably quite a lot. Due to the torque of the wrx engine. You would need engine/gearbox/drive shafts/engine mounts/custom exhaust/wiring loom. virtually everything underneath the body! Should have just bought a WRX mate lol Would have been easier and cheaper!

upgrading the engine from the linear to the aero (wrx) will be expensive and not worth it , it would be much cheaper to sell your car and buy an aero.
to do the swap you will need at least long block ( the entire engine), all electrical, ECU, gauge cluster, hood ( unless you go front mount) , exhaust.
Maybe next car :)

the two cars are exactly the same.The saab flat four is the same as the subaru flat four, that is the whole purpose of the car. theres no need to swap out the motor. If you are linear just go turbo thats all you need to do especially if you have a 2.5, you will make very good power, tq and hp.